The present invention relates to multi-spot-beam satellite communication systems, and more particularly to a satellite payload arranged to provide broadcast and surge-capacity capability to multi-spot-beam satellite communication systems.
Generally, an emerging use of wide-band communication systems employing extremely high frequency Ka or V frequency bands is leading to development and implementation of commercial satellite systems which support a large number of high-gain spot beams. Because of high reuse of the available frequency spectrum, spot beam technology advantageously allows high capacity systems to be realized with a finite number of beams. For example, the primary frequency spectrum of the orbit slot is typically divided up equally among several spot beams to form a frequency reuse cluster, e.g., four beams per cluster. Spot beam technology also permits reduction of ground terminal size to a point where such terminals become commercially feasible as a mass-market end-user terminal.
In known payload designs for multi-beam systems, total capacity of the satellite is generally divided and allocated among the beams on a preferably equal basis so as to accommodate design simplification and cost reductions as well as changes in user demand and market needs. As a result, such payloads achieve maximum total throughput only when used in support of point-to-point (PTP) transmissions having an even traffic distribution among the respective beams at their individual full capacities. However, such even distribution is inherently unrealistic because certain geographic areas naturally have a higher use demand than others. In addition, changing market conditions and other networking factors directly impact the distribution of a system""s traffic load. Thus, known multi-beam systems operate with a significantly reduced effective utilization of the satellite capacity when compared to the capacity with which the beams could otherwise collectively support.
Another drawback to known multi-beam systems and payload designs which are inherently suited for PTP transmissions is the loss of throughput efficiency when such systems are used to support broadcast transmissions to be sent to the entire geographic service area. Typically, such systems can only provide broadcast capability if the desired broadcast information is individually transmitted on every spot beam in the system.
Therefore, it is an object of the present invention to provide a multi-spot-beam satellite communication system and method having improved utilization of system capacity.
Another object of the present invention to provide a payload design for a multi-spot-beam satellite communication system which can support both point-to-point and broadcast transmissions at an optimum transmission efficiency.
Still another object of the present invention to provide a payload design for a multi-spot-beam satellite communication system which can flexibly utilize up to all of a system""s broadcast capacity as a surge mechanism to support point-to-point traffic for either uplink or downlink transmissions for any spot beam whose capacity has been exhausted.
In accordance with these and other objects, a first aspect of the present invention provides a method of configuring a satellite payload for use in a multi-spot-beam communication system including the steps of providing a plurality of spot-beam uplinks each of which receive signals transmitted from a particular section of a total geographic area to be serviced by the communication system, providing a plurality of spot-beam downlinks each of which transmits signals to a particular section of the total service area, and providing a broadcast downlink which transmits a single wide-area beam to the total service area. Point-to-point services are supported by routing point-to-point transmissions received by the plurality of uplinks to a particular one of the plurality of downlinks, while broadcast services are supported by routing broadcast transmissions received by the plurality of uplinks to the broadcast transmission link in a non-blocking manner. In addition, the method further can include the step of providing a surge mechanism by routing to the broadcast downlink point-to-point transmissions of any of the plurality of spot-beam uplinks and spot-beam downlinks whose transmission capacity is exhausted.
In accordance with another aspect of the present invention, a payload for use with a multi-spot-beam communication system includes a plurality of receiving spot-beam antenna subsystems each arranged to receive signals transmitted from a particular section of a total geographic area to be covered by the communication system, a receiver means connected to the plurality of receiving spot-beam antenna subsystems for converting each received signal to an intermediate frequency, and a plurality of transmitting spot-beam antenna subsystems each arranged to transmit signals to a particular section of the total service area. An on-board processor is connected to the receiver means and the plurality of transmitting spot-beam antenna subsystems for selectively routing received signals to a particular transmitting spot-beam antenna subsystem. A broadcast transmitter subsystem is connected to the on-board processor and arranged to transmit signals to the total service area, while an input-filter-switch-matrix is connected to the receiver means and the on-board processor for selectively routing bands of received signals to the on-board processor in a non-blocking manner for transmission by the broadcast transmitter subsystem.